Testing apparatus for compressing resilient masses



July 27, 1943. H w ANWAY 2,325,027

TESTING APPARATUS FOR CDMPRESSING RESILIENT MASSES I Original Filed Jan. l5, 1940 3 Sheets-Sheetvl I I I I I I I I I I I I I I I I I I I r I I I I l l l E:

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'Pou/v0.5 PEA SQUA/Pf F007- July 27, 1943. H. w. ANwAY 2,325,027

TESTING APPARATUS Fon coMPREssme RESTLIENT MAssES original Filed Jan. 15, i940 -3 sheets-sheet 2 lge' 5PM/N6 BICI( FOOMGE July 27, 1943.v H. w. ANwAY 2,325,027

TESTING APPARATS FOR COMPRESSING RESILIENT MASSES original Fiied Jah. 15. 1940 s' sheets-*sheet s Patented Jul-y 27, 1943 TESTING APPARATUS FOR COMPRESSING RESILIENT MASSES Herman W. nway, Cloq'uet, Minn., assignor to Wood Conversion Company, Cloquet, Minn., a

corporation ofDclaware Original application January vl5, 1940, Serial No.

2,325,027 I" i l `313,920. Divided and this application October 8, 1941, Serial No. 414,078

'1 claims. (omas-12)' The present invention relates to apparatus for testing materials, and in particular fibrous materials, by the method disclosed in my earlier application Serial No..313,920, filed Januari/ 15, 1940, of which the present application is a division, and in which the apparatus is disclosed.

j Heretofore, apparatus has been .provided to slowly compress a material in a testing operation. In studying the properties of fibers, such as Wood lfibers and others' having properties permitting them to be felted, it was discovered that the known felting of fibers resulting from compressing them, is not an immediate response to compression. Upon immediately compressing a massv of fibers, it exhibits an elasticity, which is l slowly dissipated by the elastic lforce being expended in accomplishing felting.

Asset forth in said early application, the elastic, felting and other properties of fiber may be determined by a suitable procedure involving a timed slow compression and a sudden release of the compressing force in such a way as to permit an immediate spring back of the fiber. A full explanation of the process yis not repeated here, but the process is given in sufficient detail to permit its practice. The purpose of the present application is to'claiml the apparatus develvoped -for such test and useful in testing other materials as lfor example, wherein the response to compression lags behind the compression.

It is an object of the invention, to provide a device which may be-used slowly to compress a material by the action of an advancing member,

and to provide for immediately withdrawing the.

advancing member.

Another object of the invention is to provide vone or'more auxiliary containersfor use with ing description and explanation ofthe invention, as illustrated by the accompanying drawings in which:

Fig. 1 represents a simple piece 'of apparatus vplatforms I5 and I6.

for the purpose of simplifying the explanation of the entire procedure.

Fig. 2 represents a practical apparatus in which a single compression unit is utilized with two different containers as shown in Fig. 1.

Fig. 3 represents in cross-section on line 3 3` of Fig. 1 a mechanical device permitting sudden Fig. 7 is a diagrammatic explanation used asl a short-cut explanation of determining elasticity. -.F'ig. 8 is a-diagrammatic explanation used as a short-cut explanation of determining felting.

In describing the'use of theapparatus, particular reference is made to its use on bers,`but it is to be understood that other uses are not excluded. l

From the description it will be appreciated that the structure permitting immediate withdrawal of the moving plunger, andthe constant speed of compression, are important features in the utility of the apparatus to `test fibers.

In Fig. l sufficient elements for the test are shown in use at one time, for the purpose of explanation. A surface or bench I0 has two platform scales II and I2, with dials I3 and I4 and hand wheels 2'5 and 26. 'I'he screws at their endsl rotatably carry at 2l and 28 flat plates 29 and Sli-.which fit loosely inside the cylindernon-rotatabiy with respect to the frame and cylinder when held by frictional contact with material in the container. Beneath the plates are shown test specimens 3| and 32 of ber taken from the stock to'be tested.

There are coiled compression springs 3 3` and* 34 around the threaded shafts 23 and 24, and l between the frame 20 and the hand wheels 25 and 26. These may function to raise the plates On platforms I5 and I6 29 and y30 quickly from the fiber upon release fromorgof the nut devices 2| and 22.- The nut devices are constructed to permit this. While it is possible to release the nut from its engagement with the frame, to raise the screw, it is preferred to release the engagement of the nut and the threads of the screw. This may be accomplished by using a nut device which has two portions relatively movable for accomplishing this. Each nut is made in two portions, best shown in Figs. 3, 4 and 5. Fig. 3 shows a split nut having the complementary portions 35 and 36 (Fig. 5), with bases 31 and 38 which slide in guideways. On the frame 20 (Fig. 4) is secured a block 39 having a recess in which the bases 31 and 38 are slidable. Strips 40 and 4| are held by screws to the block 39, forming guideways for sliding the two nut portions toward and away from each other. There is a circular opening in the block 39 for receiving a disc-like body 42 with a handle 43 projecting through an opening 44- in the block 39. Arouate slots 45 cut into disc 42 serve as cams on pins 46 mounted on the bases 31 and 38. Thus moving handle 43 to position (dotted line) 43, opens the splitnut structure to permit disengagement of the screw and nut, and the action of the springs to raise the compression plates.

The test specimens or masses 3| and 32 are shown as compressed to the same density, and the plates are at the same height in the cylinders. This is the result of using weights of specimens 3| and 32 to be tested, that are in proportion to the ultimate ber volumes 3| and 32 shown in Fig. 1, where the columns have the same height, and hence the weights are proportional to the cross-sectional area of the cylinders, and to the densities of the fiber masses. For example where the radius R is 4 inches and the radius r is 1% inches, the weights have the ratio of V(i4/to 9. In practice for woodber in such cylinders, the actualweights chosen are 158 grams for the large cylinder and 22 grams for the small cylinder.

In making a test predetermined masses of the material to be tested are placed in the cylinders and the plates slowly moved to compress the samples. The rate at which compression occurs is arbitrary and not important. However, it is important that both masses of the material should be compressed at the same rate,

and that the rate be uniform and standardized for comparisons, where a series of materials are involved. This may be done by power means (later described). If the reading of the scale I3 or I4 is plotted against density of the sample there is obtained a characteristic curve of exponential form which will be later referred to. A final observation is made on both masses when they reach the same arbitrarily selected density. If the pressure is released by moving both plates upwardly in the cylinders, there will be seen a spring-back" or expansion of the compressed masses 3| andA32 to new positions. This arises `from a resiliency of the fiber. An important difference in each cylinder thus becomes apparent. The expansion is not the same in each case. The density at expansion in the large cylinder is recorded as an importannt figure for calculations.

The failure of the two masses to showlthe same proportional spring-back is cause for inquiry, introducing certain principles involved in the test. When constantly moving pressure is placed upon a sample of fiber in a cylinder, work is done. This is utilized inl overcoming the sliding friction of the mass on the cylinder wall,

in overcoming elasticity of the mass as a unit, and in overcoming the internal friction between the bers within the mass., involvingv shifting position and even breaking of fibers. Felting is the result of internal changes, and it is related to elasticity. Therefore, the recorded reading of each weighing scale is a composite figure depending upon these properties.

SLIDING FaIc'rIoN When the pressure is released from the selected nal density position, there is force opposing the tendency to spring back, so that the final spring back is not an accurate indication of resiliency. One element of this force is the friction between the wall of the cylinder and the expanding mass. Naturally the results are different in the two cylinders because the area per unit volume presenting friction isl relatively greater in the smaller cylinder and its springback is less than that in the larger cylinder.

Practically, the. spring-back in the cylinders is not recorded, nor used in determining friction. The total force readings at each final compressed density are recorded for calculating friction. Let

R=radius large cylinder.

r=radius small cylinder.

h=an arbitrary column height to which both samples are compressed to have some arbitrary density.

a=component of force required to compress fiber in small cylinder, excluding component to overcome sliding friction.

b=component of force required to compress fiber in large cylinder, excluding component to overcome sliding friction.

c=component of force to overcome sliding friction in small container.

d=component of force to overcome sliding friction in large container.

f=flnal scale reading for small cylinder.

F=nal scale reading for large cylinder.

Then:

(1) f=a+c (2) s F=b|d Because compression is a volume effect, then y a r2 b"= 2 O1' a=R2 Because sliding friction is a surface effect, then (4) l -=1r or c=i1 Therefore, using (3) and (4) in (1) hr2 dr (5)y f Rfi- R But 6) l=k' which is a xedconstant for two selected cylinders. Substituting the value lc in (5), then (7) f.-..bk2+dlc Solving (7) and (2) simultaneouslyl fkli' JZ-k-lc2 For the specific cylinders (8 inches and 3 inches diameter) described, the value k maybe substituted to give f (8) d=4.269f--.6F

Solving (8) and (4) (9) c=1.559f-.22F

In the small cylinder of radius i', the force on the plate which compresses the fibers is a, and the force sliding the fibers is c. Consider an area to be tested as a unit area in a circular band of the fibers compressed to height H. Then the sliding force f' on the unit area is expressed:

In small-diameter vcolumns it is approximately true that the said unit area exerts on the container wall the same unit pressure P as is exerted upon it by force a. 'Ihis is expressed:

Let K=a coefiicient of friction, which in usual terms is the force which slides any two contacting surfaces divided by the force holding the surfaces together, or

Therefore, from (11) and (12),

(2T K=m A In the same way, for the large cylinder The formula for the large cylinder is used in actual practice as wherein d is given in (8), his the column height, and b is found from (2) in terms of F and d.

EXAMPLE- Woon FIBER (For practical and mathematical convenience the density is expressed as its reciprocal unit in terms of footage or board feet per pound of ber, one board-foot being 12 x 12 x 1 inches). In the B-inch cylinder is placed 158 grams of wood fiber, which is equivalent to 1 pound per square foot of cross-sectional area. This is compressed at a constant rate of 1 inch in 32.4 seconds to a column height (h) of 2 inches, or 2 board-feetper pound, with 'a pressure on the scale of 240 pounds. (The remaining operative procedure is omitted at this point and introduced later where itis pertinent.)

i In the small cylinder is placed 2 2 grams of the l same fiber, which is compressed at the same rate to the same nal footage of- 2 board-feet per pound, at a'nal pressure of 41 pounds. "I'hus, the values neededare F==240 p 1:41 4 Using (8) d=4.269 411.6 240=32 Using (2) b=24032=208 `Using.(15) the coemcient of friction is ELASTICITY Using the larger cylinder for data in determinlng compressive properties, depends upon the fact determined by many experiments that there is a simple mathematical relationship in experimental columns of small diameter, when a given procedure is used. Thus, it has been discovered with respect to the 8-inch cylinders and smaller cylinders, that a given rate of' compression produces a substantially logarithmic relation between the footage of fiber and the compressive force as compression occurs.4 For an 8-inch cylinder the curve is practically useful, even though it departs but slightly from a true logarithmic relation. This will best be understood by applying data of Table I measured in compressing the fiber in the -inch cylinder as given in the example. In Table I:

by a factor 2.86 to adjust the data to a similar column having one pound of ber over a crosssectlonalarea of l-square foot. I'he purpose of this is to bring certain of the ultimate values to be reported in units of pounds per square-foot.

Table I Column l Column 2 Column 3 FceSiix h Ad poun s, nc )usted force gaggufg diameter in pounds,

158 gram l lbs. specimen specimen 8.5 75 2. 14 8. 0 l. 25 3. 6 7. 5 1. 75 5. O 7.0 2. 75 7. 9 6. 5 4.0 1l. 4 6. 0 6. 5 15.7 6.5 8.5 24.3 5. 0 l2. 5 35. B 4. 5 19.0 54. 5 4. 0 30. 0 85. 9 3. 5 47. 0 l34. 5 3.0 80.0 228. 5 2. 5 130.0 372.0 2.0 240. 0 686.0

Obviously, the plotting of column 1 against column 2 or column 3 willgive the same mathe-l matical relation. A direct plot has little visual But if the logarithms of either of column 2 or 3 are plotted against direct values of column l, it is possible to draw a.r mean straight line which is mathematically useful. This line is mathematically significant of a defl- .nite order of changesin compressing. In Fig. 6

column 3 of Table I isv plotted vertically on a log scale 48, and column 1 is plotted horizontally on an arithmetical scale 49. The circles are the measured data, and straight lineV 5U is drawn as 4the mean line of lthe data. A smaller cylinder produces less variation. Errors in observation explain part of the deviation. Line 50 is called the C-line for brevity, meaning the line of,com pression.

Another and related mathematical relation has been discovered. When a column of fiber is compressed to various heights at a selected but arbitrary regular rate of compression, and the pressure is released to permit immediate expansion, the height of the column on return and the height before return have a definite relation. By reason of the relationships established above, there is also a definite relation between the height after spring-back, and the force released to permit spring-back.

Table II gives an illustrative set of such readings taken at ya regular rate of compression o f 1 inch in 32.4 seconds and at immediate release during compression, in the large cylinder above described. The rate of compression is the same as used for Table I, in the B-inch cylinder, using for each test, new batches of the same fiber used in the example.

For each action of spring-back, there is a compression reading (column 2) which is released and there are data of column heights before and after release.l 'There is also a compression reading on the original compression curve corresponding to the spring-back height. These two observed and read compression values, adjusted to a one pound mass of fibers may be found in the adjusted values of the plot of the C-line 50. Thus, at the ordinate value in Fig. 6 which corresponds to either selected one of the two said compression values, a horizontal line may be drawn with its terminals determined vby the abscissae values, which are column heights. The compression reading at the spring-back height has been selected as the ordinate for drawing each said line.- Such horizontal lines are represented by the lines 53, whereby they fall under and terminate at their right ends in the C-line.'l The other ends of these lines also indicate a substantially straight line which tends t intersect the horizontal axis 49 (which is 1 and not zero on the log scale 48) at the same point 54 where line U intersects it. Taking this experimental tendency as a mathematical truth (justified later), and using the final density of footage 2 (Table I) andits spring back (the top-most line 53) and the intercept 54, the straight line 55 is drawn for graphic use. Line 55 is termed for brevity the Cs-line, meaning that it i's determined by compression and spring-back. -The abscissa of vertical line 56 represents the one measured spring-back footage needed for actual work.` The common intercept 54 with the axis is significant. The mathematical significance of the Cs-line will be later explained.

i Mathematically, the point 54 represents the footage at no applied force of compression. Pracsion at all because the bottom of the mass is sion, at all because the bottom of the mass iscompressed by thefibers above. The value is the result of extrapolation, and is herein considered as an absolute value, called free-footage, or the density at zero compression. It has been noted that the log scale reads 1 at the line of scale 49. The force actually exerted at zero compression on the device (weighing scale) registering the plotted pressure values, is the weight of the ber. Since column 3 of Table I is plotted on log scale `48 after conversion to a one-pound specimen, the intercept 54 is taken as a practical finite and absolute value, because at no compression the ber will register in fact one pound on the weighing scale. Obviously, at this condition it can have no spring-back, and hence line 55 must pass through point 54. It has been found that many apparently uncorrelatable properties of a series of different fibers become correlated when plotted against free-footage. The freefootage value has thus been found to be a measurable significant property of a fiber mass independent of its state of compression. The freefootage may combine other fundamental values,

but in itself, it is capable of simple determination.

To determine it, reliance is placed upon the mathematical truths which obtain with the selected conditions establishing them, as above described. It has been found to be a satisfactory procedure to record a series of observations as given in Table I.. sufiicient to locate a mean straight line. observations will sufllce. By releasing the ber for spring-back, from a nal compression point,

such as 2 board-feet, the spring-back value deter- 1 mines one point of the Cs-line of which the freefootage intercept is known to be another, thus determining directly the Cs-line. Therefore, in the example, when 2-board feet is attained, the compression is released, and the spring-back recorded to determine the Cs-line 55.

The Cs-line, which is a mathematically convenient force line, is capable of interpretation to give useful information. The obvious application (and basis for drawing the Cil-line) is to indicate the spring-back footage from any compressed footage. The Cs-line interpreted as a force line indicates the summed forces lost in irrecoverable work. Where vertical line 56 at footage 3.8,. as actually measured after spring-back from footage 2 crosses Cs-line 55, it is thus read on the Cs-line 55 that 37 lbs. were lost in irrecoverable Work; that is to overcome sliding friction and in producing felting. However, where line 56 crosses the C-line at a footage of 3.8 it is read that lbs. were used in overcoming resistance to elasticity, sliding friction, and in producing felting. Since the felted condition in these two circumstances is substantially the same, and since resistance to slidingV friction during compression from 3.8 to 2 footages and in expansion from 2 to 3.8 footagesis substantially the same, it follows that the elasticity opposed the compressing force to the extent of the difference between 130 and 37 at 3.8 footage, or 93 lbs.

The graphic relations may be claried by a short--cut diagrammatic illustration. In Fig. 7 three columns of fiber are illustrated at heights corresponding to the footages indicated on the scale at the left of the gure. The blocks 58 and 59 with their arrows at the top indicating a force on each column, are taken directly from the For very crude work, two such C-line. The block 59E is the block 59 at its expanded height as read from the Cil-line.

It is important to note that if the compression process is halted and the confined material allowed to stand ina static condition, 4internal changes take place, not, immediately, but rather slowly. This may be measured by drop in pres- 'sure until it becomes small. The rate, at which this occurs'may also be determined for comparisons. Thus kinetic elasticity is converted into "felting by the expansive force expending itself internally in rearranging fibers to a stable or static condition. The potential elastic energy which isimmediately available while compressing becomes largely lost on standing with the liber mats confined at a fixed volume, the lost energy becoming fixed as felting energy.

From the foregoing it is obvious that in comtor 2.86 for the graphical chart on the l-pound pressing the" ber, work is done upon it; that if the compression is immediately releasedI a part of that work is recoverable; and that if the pressure is halted without release'the said recoverable Work becomes less and less recoverable as time goes on to a point where ipractically none is recoverable. Thus, the work input goes to overcoming sliding friction, to overcoming elasticity, and to producing felting. That .which overcomes elasticity may be converted to felting by standing under a suitable4 load xedly to confine the mass.

Thus, block 58 on standing will become static .and substantially like block 59E. The felted conditions in blocks 59 and 59E are substantially the same. Block 59 in expanding to block 59E gives up energy because of Aits instant elasticity and 4produces a static block 59E in which the felting energy is the same as the summed energies of felting and elasticity in block 58. The force required at footage 3.8 (block 59) to effect this con version is the difference between 130 and 37, or 93 pounds as the elastic'force instantly recoverable from block 59, as it is being initially compressed. Thereiore, the value -93 may be taken as the instant elastic force in the initial compression at 3.8 footage.

Point 63 is plotted on the 3.8 footage line 55 at 93 lbs., and a straight line 64 is drawn from point 63 to point 54. This line is the plot of specific elasticities for the various footages, there being obviously no elasticity at the free footage point 54. This line 64 is called the specific elastic-line or KE-line. Its slope is a constant which is taken as the absolute elasticity of the fiber. As pointed out there is no specific elasticity at the free footage condition, and the speciiic elasticity varies according to the degree of compression. But the rate at which these vary is indicated by the slope of the Kil-line. Experience with many ber masses shows this slope to bea characteristic property of the particular ber as tested herein for comparisons.

The slope of a straight line is readily determined by known mathematical procedure. Select two points on the line. Divide the difference in their ordinate (y) values by the difference in the abscissae (1:) values, and the result is for line 64, the value .377. This is the absolute elasticity herein termed ME, for which the minus sign may `be neglected. However. as the absolute elasticity.

it eliminates the degree of compression.

FELTING The total applied compression force after tak-` ing out that for elasticity, gives a residue involvbasis, the sliding friction fonce at footage 2 is 91.5 pounds.

Thus, at vfootage 2.00 in the compression, 91.5 lbs. of the C-line '101 lbs. is used to overcome slidlng friction for the chart of Fig. 6. Experience has shown that frictional forces at other densities form a substantially straight line in Fig. 6, passing through the point 54 of free footage. Accordingly, point 66 is plotted at the values footage 2 and 91.5 pounds. Line 61 connects points 54 and 68, and represents the speciic frictional forces at the different footages.

There is approximation for practicality in directing the friction line 6l to be drawn to the 'free-footage point 54. In reading values on the friction line 61, one should not overlook the fact that at the point 54 the ordinate value on the chart Fig. 6 is 1, which is zero compression, but it is the scale reading resulting from the weight of the fiber. Therefore, at point 54 one does not read that the friction value is l pound, but rather it is read as zero. The deduction of one from the ordinate values of line 61 is ignored at'the higher values winch occur in the practical work.. ing range, because it is less than the experimental errors in the process and in the calculations. For example, at=2board feet per pound, at the point 66, the value can hardly be read irom the chart any closer than one pound. At 7 board feet per pound, one would read 'on the friction line 61, 3.6 pounds from the ordinate scale, but one would know that this should be 2.6 pounds in terms of the component of the applied force to overcome friction.

The determinationv of felting may be done by graphical derivation from the lines already described on the semi-log chart Fig. 6. But the reasons are not readily obvious. The operation is best explained by a specific reference toa given condition, as in Fig. 8. Herein blocks 'I0 and 'il represent the column being initially compressed. Block l2 represents block l I originally at 2 board. feet, sprung back to 3.8 board-feet. Block l0 has been chosen at 3.8 board-feet on the way down to 2 board-feet. From C-line 50 (or the original data) it is known that 130 lbs. pressure is required in the original compression to attain 3.8 board-reet. From the friction-line 61 it may be read that at this point on block l0, 28 lbs. is used to overcome friction. This leaves a balance of 102 ibs. which is overcoming elasticity andv producing felting. It has been stated that ii' block lllwas allowed to stand the same would become static and practically like block 12. Thus practically all or' the 102 lbs. would eventually go into felting energy. Therefore 102 lbs. is taken as the force component going to felting energy in the static block 12, or in the block 'I0 when it becomes static. However, block I2 became static by expansion from the condition'of block Il The felting in block 12 therefore existed in block 'H while the block 'il was elastic. Accordingly, the

102 lb. represents fairly accurately the force component going to felting energy of block 1I at 2 board-feet. It is therefore the determinant for the felting line, the slope of which is taken as the absolute felting property of the fiber, giving its felting property independently of degree of compression or state of felting. By plotting the point at 102 lbs. and 2 board-feet, and by drawing line 18 from point 15 to point 54, the resulting felting line, or the KF-line, represents specific feltlng values at any footage, as well as a constant for felting. Thus, at 3.15 board-feet the felting force is 48'1bs. The slope of the curve is -.286, which is the absolute felting property, orV

constant Mr. The minus sign may be neglected.

To solve graphically in the simplest way for the felting curve, given the C-line `5l), the sprung footage from nal compression, the nal compressed footage, and the friction line 61, proceed as follows:

Where the sprung-footage line 56 in the plot Ycrosses the C-line 50 and the friction line 61,

vsubstract the ordinate valuesof the two intercepts and plot the difference as a. point on the line of the footage from which the spring-back took place, or in other words at the footage existing at the end of the experimental compression. Draw a straight line from said plotted point to the free-footage point 54. This line gives the specific felting at each footage plotted, and its slope gives the absolute felting property.

SPECIFIC CoMPARIsoNs For practical purposes fibers may be compared at some arbitrarily selectedhfootage, which is chosen as one close to useful footages. Thus,

arbitrarily, comparisons are made herein at 3.15

footage and the values given as specic" are selected at this footage. drawn at 3.15 footage and designated specific footage for reading off specific Values.

Table III Absolute Speeltlc at 3.15 Property board feet Line 80 in Fig. 6 is- 9 board-feet per .377 (a coecient .286 (a coefficient). .308 (e coeiicient) pound.

Friction 1 Only a corrective value.

The above described process has been applied 2,145,851, with and without various treating materials employed in the Asplund machine according to Asplund Patent No. 2,047,170. In particular, it has been found that the "free footage is a property which correlates variations in samples, treated or untreated, better and more signiflcantly than any other property. Fibers such as of Palco wool, chemical or semi-chemical wood pulp, mineral wool, cotton, cotton linters, jute, kapok, red wood bark, MacMillan fiber, and others have been tested by the invention for comparative purposes. Wood fiber fractions and mixtures of fractions have been tested to produce a bermass of specific properties.

The invention is subject to many variations, but where comparisons are made a set procedure is adopted. This calls for specifying the rate of compression,' the densities of ber at which data are taken, the sizes of containers and the weight of fiber for each container.

'I'he following is a summary of procedure, devoid of explanation made herein for the purpose of transfer bodily to other applications for patent which will involve reference to this application, and use of a procedure within it. The details given are therefore not limitations.

PRACTICAL PROCEDURE Place 158 grams of loosened fiber in a cylinder of S-inches diameter and 22 grams of thesame loosened fiber in a B-lnch diameter cylinder presenting the same character of interior surface. Place the cylinder on a platform scale adjusted to read zero (or else the weight o-f the fiber, the difference being negligible). With a -at plate compress the large column of fiber at the rate of 1 inch in 32.4 seconds until it is 2 inches high (a reciprocal density of 2 board-feetper pound). Record the pressure on the scale as reading P pounds, and the corresponding height of the column, at approximately each half-inch of advance, or a suicient number of observations to locate a mean straight linel Record the final pressure Q at column height of 2 inches. Upon attaining said last mentioned height, immediately remove the plate to release the column. Measure the height (board-feet per pound) attained by the column after such spring-back, and record as H inches (or board-feet per pound).

Then substitute the smaller cylinder, and compress at the same rate until the column height is 2 inches (board-feet per pound), and record the pressure as R pounds.

The following data are thus obtained: p

Table I V Board-feet per Footage on S-inch 3-inch pound or "lootage spring-back s'iuch column column H Re 2 Q (The series) (The series P) Select semi-log graph paper having a. log scale vertically beginning at log of 1, (which is zero), and mark equal divisions of footage units horizontally. On the chart, plot the series of observations using P 2.86 and the point: 2 footage and Q 2.86. .Draw a mean straight line through these points. Where the line cuts the bottom of the chart (at l), designate the point and the reading as free footage. Label the straight line C-llne, or compression line."

From footage H on the C-line draw a horizontal line to a point of intersection with the line for footage 2. Draw a straight line from this point to the free-footage and label the line CB-line, or spring-back line. Draw a vertical line at H footage and label sprung-back footage. On the latter line, subtract the ordinate values of the intercepts with the C-line and Cs-line, and record the difference. Mark this difference on the log scale as a point on the H-footage line, draw a straight line from the point to the free footage point, and. label K-llne." Take any two points on the KE-line. Subtract the ordinate values (the log units, not the pounds) and divide the difference by the difference of the free-footage values. Neglect the minus sign and record the value as ME or the Absolute elasticity. Draw a vertical line through 3.15 footage and mark specific footage."

Aasesorar footage line, record the force value as the "spesolve for y. Using the formula (wherein K=co efcient of friction) 1 assale-13o T assale splve for thevalue K. On the vertical line for footage of 2, plot the value of y, and draw a straight line to the free footage, marking the line "friction line." On the friction line at H-footage record the force value as a deduction value. On the C-line at H-footage read the force value, subtract from it the said deduction value', and record the difference as felting at 2 board-feet." Plot this felt- Ving value on the vertical line for 2 board-feet, connect the point by a straight line with the freefootage point, and label the line "Kr-line or felting line." Determine the-slope of the Kr-line by dividing the difference in ordinate values (the log units, not the pounds) lofptwo selected pointsy in it by the difference .in footage values of said two points, and label the gure so obtained with or without the minus sign as absolute felting" or Mr." At the specificfootage on ,the Kil-line record the force value as specific felting. Thus the values determined are compressive properties, listed in VTable V.

Table V Specific values (at 3.15 I Absolute values footage) Freo footage Absolute elasticity (M s) Absoluufclting (Ms-L Cuvilivivut friction (K) Specic elasticity (Kn). Specific iclting (Kr).

ACCURACY or RasuLrs vThe figures obtainable are obviously not precise, due to errors in observation, errors in sampling (two containers), and approximations of -fact upon which the procedure is based. However, there is a fair and useful check, making the results useful for comparison. It is pointed out that both the mechanical and the graphic procedures are quick and simple. The log chart Fig. 6 is a key to a system of straight lines for graphic solutions. True mathematical derivations would require the Kaz-line, the Kia-line, and the friction line B1, to curve downwardly and approach zero value at infinity on the log ordinate scale, thus making the loci of the lines mathematically indeterminate from the one springback operation. By the expedient of adding the value one to the true values. and thereby locating the lines through the free footage point 54, the lines become straight lines for practical usage.

PRAcrxcAr. APPARATUS In practice a simple testing machine is used with a power driven motor to provide a constant rate of compression. The two cylinders are used at different times with change of presser plates. Such a machine is shown in Fig.' 2. It has a base |0|, a U-frame |02, a platform scale |03 set on the base, with force-dial |04. A split nut structure |05, as described for Fig. 1, is mounted on frame |02. Screw |06 is threaded to engage the nut, and grooved at |0I'to receive gear |08 which is splned into said groove. A motor |09 has a worm gear ||0 meshing with gear |08. Spring is compressed between a head ||2 on the screw shaft |06, and serves also to hold the gear |08 against frame. |02.

either cylinder I1 or I8, and the letter P represents the corresponding presser plates 29 or 3D- An important use of the compressive propery ties relates to the choice of particular machines to make fibers, or the operation of a single machine. For example, given two machines A and B according to Asplund Patent No. 2,145,851, of two different diameters of grinding plates, it has been determined that fiber made from both machines of the same wood','having substantially the same average particle size, have entirely different compressive properties. Thus machine A gives fiber characterized by a much lower coefficient of sliding friction, higher free footage, speciflc elasticity and specific felting, and lower values of absolute elasticity andabsolute felting.

It has been determined by fractionation of such two fibers that the particle size distribution is different. Different fractions of fibers have been tested for their compressive properties, and in general there is a systematic change in these properties according to progressive Aranges of sizes in the fractions of a fiber mass.

In the claims, only the apparatus-is defined as the invention, the method of using it for fibers, being claimed in Serial No. 313,920, filed January 15, 1940, of which the present application is a division.

l claim:

1. Apparatus for testing feltable fibers comprising an axial container in which to house for compression axially a columnar mass of fibers, a presser relatively movable axially into said container and adapted to press only upon the end of a column of fiber, said presser being normally biased to move relatively away from said container axially thereof, means for so relatively moving said presser and said container at a constant predetermined rate in compressing the ber column in the container, indicating means adapted to register the force exerted by said column while being compressed, means adapted Yto be released to free the presser from the compressing force whereby the normal bias of the presser effects immediate separation of the presser and the compressed column of fibers to halt the compression thereof and whereby the compressed column may freely expand, and means to indicate the height of the compressed and the expanded column in the container.

2. A testing device comprising a supporting frame, a nut member in said frame, a threaded shaft through said nut member to be advanced axially by relative rotation of the nut and shaft, a plate on the end of the shaft for advancement therewith while 'otherwise stationary with respect to the frame, said frame providing space -ahead of the plate for a container into which l The letter C designates the said plate may advance, means for releasing the engaged relation between the nut and shaft,

and means providing a moving force for reversing the advancing plate upon release of said engaged relation at any point in its advance whereby any material in the container being compressed by the plate is free to expand.

3. A testing device comprising a supporting frame, a nut member in said frame, a threaded vshaft through said nut member to be advanced s frame, a nut member in said frame, a threaded shaft through said nut member to be advanced axially by relative rotation of the nut and shaft, a plate on the end of the shaft for advancement therewith while otherwise stationary with respect to the frame, said frame providing space ahead of the plate for a container into which the said plate may advance, a gear splined onto said shaft, a motor connected to rotate the gear to move the shaft axially in one direction, said nut member being constructed with at least two parts relatively movable whereby it may be disengaged from the threads of the shaft, and spring means to move the shaft axially in the other-direction upon disengagement of said shaft and said nut member.

5. A testing device comprising a supporting frame, a shaft mounted in said frame to move axially, a plate on the end of said shaft for advancement therewith while otherwise stationary with respect to the frame, said frame providing space ahead of the plate for a container into which said plate may advance, means to move said plate at a constant linear speed, said means including a disengaging ldevice for breaking the moving connection between said shaft and said means and to release the shaft for free axial movement,- means associated with said shaft to withdraw it from itsdirection of advance upon release of the shaft, means to measure the comy pressive force on material in the container, and means to measure the height of material in the container.

6. A testing device comprising a frame, an axially movable member mounted on said frame providing an advancing pressing surface, said frame providing space ahead of said surface for a container into which said member may advance, means to move said member axially to advance said surface at a constant linear speed, said means including a disengaging device for breaking the moving connection between said member and said means and to release the member for free axial movement, means associated with said member to withdraw it from its direction of advance upon release of ,the member, means to measure the compressive force on material in the container, and means to measure the height of material in the container.

7. Apparatus for testing material comprising an axial container in which to house for compression axially of the container a column of material to be tested, a presser relatively movable axially into said container and adapted to press only'upon the end of said column of material, said presser being normally biased to move relatively away from said container axially thereof, means for so relatively moving saidpresser in said container at a constant predetermined rate in compressing the column in the container, indicating means to register the force exerted by said column while being compressed', means adapted to be released to free the presser from the compressing force, whereby the normal bias ofthe presser effects immediate separation of the presser and the compressed column to halt the compression thereof and whereby the compressed column may freely expand, and means to indicate the height of the compressed and the expanded column in the container.

HERMAN W. ANWAY.

CERTIFICATE OF CORRECTION l Patent Ne. 2,525,027. VJuly 27, 19,45.

HERMAN W. ANWAY.

It is hereby certified that error appears in the 'printed specification of the above numbered patent requiring correction as follows: Page lq., second column, line 5, strike out Sion at all because the bottom of the mass is and insert instead -tica11y, fibers cannot be massed at no compresand that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 51st day of August, A. D. 19H5.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

